1. Field of the Invention
The present invention relates to a resist composition for negative development and a method of forming a resist pattern using the resist composition for negative development.
Priority is claimed on Japanese Patent Application No. 2011-083799, filed Apr. 5, 2011, the content of which is incorporated herein by reference.
2. Description of Related Art
Techniques (pattern-forming techniques) in which a fine pattern is formed on top of a substrate, and a lower layer beneath that pattern is then fabricated by conducting etching with this pattern as a mask are widely used in the production of semiconductor devices and liquid crystal display devices. These types of fine patterns are usually formed from an organic material, and are formed, for example, using a lithography method or a nanoimprint method or the like. In a lithography method, for example, a resist film is formed on a support such as a substrate using a resist material containing a base component such as a resin, and the resist film is then subjected to selective exposure of radial rays such as light or electron beam, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. Using this resist pattern as a mask, a semiconductor device or the like is produced by conducting a step in which the substrate is processed by etching.
The aforementioned resist materials can be classified into a positive type and a negative type. A resist material in which the exposed portions exhibit increased solubility in a developing solution is called a positive type, and a resist material in which the exposed portions exhibit decreased solubility in a developing solution is called a negative type.
In general, an aqueous alkali solution (alkali developing solution) such as an aqueous solution of tetramethylammonium hydroxide (TMAH) is used as the developing solution (hereafter, a process using an alkali developing solution is sometimes referred to as “alkali developing process”).
In recent years, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beam (EB), extreme ultraviolet radiation (EUV), and X ray.
As shortening of the wavelength of the exposure light source progresses, it is required to improve various lithography properties of the resist material, such as the sensitivity to the exposure light source and the resolution capable of reproducing patterns of minute dimensions. As resist materials which satisfy such requirements, chemically amplified resists are known.
As a chemically amplified resist, a composition is generally used, which includes a base component that exhibits a changed solubility in a developing solution under the action of acid and an acid generator component that generates acid upon exposure. For example, when the above developing solution is an alkali developing solution (when the process is an alkali developing process), as the base component, a base component that exhibits increased solubility in an alkali developing solution by the action of acid is used.
Conventionally, a resin (base resin) is mainly used as the base component of a chemically amplified resist composition. Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are the mainstream as base resins for chemically amplified resist compositions that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm.
Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
In general, the base resin contains a plurality of structural units for improving lithography properties and the like. For example, a structural unit having a lactone structure and a structural unit having a polar group such as a hydroxyl group are used, as well as a structural unit having an acid decomposable group which is decomposed by the action of an acid generated from the acid generator to form an alkali soluble group (for example, see Patent Document 1). When the base resin is an acrylic resin, as the acid decomposable group, in general, resins in which the carboxy group of (meth)acrylic acid or the like is protected with an acid dissociable group such as a tertiary alkyl group or an acetal group are used.
Further, as acid generators usable in a chemically amplified resist composition, various types have been proposed including, for example, onium salt-based acid generators, oxime sulfonate-based acid generators, diazomethane-based acid generators, nitrobenzylsulfonate-based acid generators, iminosulfonate-based acid generators, and disulfone-based acid generators. Of these, as an onium salt-based acid generator, iodonium salts containing iodonium ions as cations and sulfonium salts containing sulfonium ions as cations have conventionally been used.
In a positive development process using a positive type, chemically amplified resist composition (i.e., a chemically amplified resist composition which exhibits increased solubility in an alkali developing solution upon exposure) in combination with an alkali developing solution, as described above, the exposed portions of the resist film are dissolved and removed by the alkali developing solution to thereby form a resist pattern. The positive development process is advantageous over a negative development process in which a negative type, chemically amplified resist composition is used in combination with an alkali developing solution in that the structure of the photomask can be simplified, a satisfactory contrast for forming an image can be easily obtained, and the characteristics of the formed resist pattern are excellent. For these reasons, currently, there is a trend to use a positive development process in the formation of extremely fine resist patterns.
However, in the case of forming a trench pattern (isolated space pattern) or a hole pattern using this positive development process, as compared to the case of forming a line pattern or dot pattern, the pattern formation under weak incident light intensity is inevitable, and the contrast between the exposed portions and unexposed portions in terms of the intensity of incident light is also smaller. For this reason, there is a tendency that the pattern forming capability in terms of resolving power or the like is limited, which makes it difficult to form a resist pattern of high resolution.
In contrast to the positive development process, a negative development process using a negative type, chemically amplified resist composition (i.e., a chemically amplified resist composition which exhibits decreased solubility in an alkali developing solution upon exposure) in combination with an alkali developing solution is thought to be advantageous in the formation of trench patterns and hole patterns.
In recent years, as a negative developing process, a process using the aforementioned positive chemically amplified resist composition in combination with a developing solution containing an organic solvent (hereafter, sometimes referred to as an “organic developing solution”) (hereafter, this process using an organic developing solution is sometimes referred to as a “solvent developing process”) has also been proposed. The positive chemically amplified resist compositions exhibit increased solubility in an alkali developing solution upon exposure, although the solubility thereof in an organic solvent relatively decreases at this time.
For this reason, in the negative developing process, the unexposed portions of the resist film are dissolved and removed by an organic developing solution to form a resist pattern (see, for example, Patent Document 2).